Hominin postcranial remains from Drimolen Main Quarry, South Africa

Drimolen Main Quarry (the primary excavation within the Drimolen paleocave system in Gauteng Province, South Africa) dates to ~2 Ma and has yielded abundant hominin remains. Most craniodental specimens are attributed to Paranthropus robustus, but the collection also includes a cranial vault of Homo aff. erectus and teeth with early Homo affinities. Here we catalog isolated postcranial specimens recovered between 1994 and 2015 and contribute formal descriptions along with comparative and functional analyses to provide further information on the paleobiology of the Drimolen hominins. Twenty-eight fossil specimens are cataloged, although two previously considered as possibly hominin are formally removed from that status. Like the craniodental assemblage, the postcrania include a high proportion of juveniles and subadults. Upper limb elements include an adult distal humerus (DNH 32), ulnar fragment (DNH 109, previously described), three fetal/perinatal humeri, three fetal/perinatal radius fragments, and nine manual phalanges. Lower limb elements include two fetal/perinatal tibiae, hallucal metatarsal, and nonhallucal pedal proximal phalanx. Vertebral and pelvic material include an adult lumbar centrum, a partial pelvis (DNH 43, previously described), and infant thoracic and lumbar neural arches (DNH 150 a and b). DNH 32 and DNH 43 can be attributed to P. robustus with some confidence while DNH 150a and b can possibly be associated with the DNH 134 juvenile cranium attributed to Homo aff. erectus. Although most other specimens probably belong to P. robustus, taxonomic attribution is challenging given Drimolen's mixed assemblage. Functional analyses indicate small-bodied hominins committed to terrestrial bipedality. However, the first metatarsal evinces a tight tarsometatarsal joint curvature possibly suggesting increased hallucal divergence in that individual. These results might reflect taxonomic variation or evolutionary mosaicism of the postcrania.